Cooling system for an on-board inert gas generating system

ABSTRACT

The inert gas generating system includes a compressed air source, a cooling air source, and a separation module. The separation module includes first and second inlets and outlets. The first inlet is coupled to the compressed air source. The first outlet is coupled to the first inlet via a bundle of hollow fiber membranes. The second inlet is coupled to the cooling air source, and the second outlet is coupled to the second inlet via a space surrounding the bundle of hollow fiber membranes.

This patent claims priority pursuant to 35 U.S.C. § 119(e) and § 120 toU.S. Provisional Patent Application Ser. No. 60/453,102, filed Mar. 7,2003, the disclosure of which is incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to cooling systems. More specifically,the invention relates to a system and method for cooling a nitrogenenriched air stream as it passes through an air separation module (ASM)of an On-board Inert Gas Generating Systems (OBIGGS).

2. Description of Related Art

The energy requirements of most modern aircraft are supplied bycombusting aviation gasoline, which is typically stored in fuel tankswithin an aircraft's wings. Such fuel tanks also contain an explosivefuel/air mixture in the area above the fuel, otherwise known as theullage. Accordingly, many systems have been developed to reduce thedanger of accidentally igniting this air/fuel mixture.

One way of addressing such a danger is to replace the explosive air/fuelmixture with a nonflammable inert gas, usually nitrogen. The On-boardInert Gas Generating System (OBIGGS) does just this, by separatingnitrogen from local, ambient air and replacing the fuel/air mixture inthe ullage with this nitrogen.

Military aircraft have used OBIGGS systems for many years to protectagainst fuel tank explosions caused by extreme aircraft operation andexposure to small arms fire. However, military aircraft are not the onlyaircraft that would benefit from OBIGGS. For example, investigationsinto the cause of recent air disasters have concluded that unknownsources may be responsible for fuel tank ignition and explosion.Subsequently, OBIGGS has been evaluated as a way to protect commercialaircraft against such fuel tank explosions caused by any ignitionsource.

Prior OBIGGS systems have proved relatively unreliable, heavy, andcostly for both initial acquisition and non-military operation.Accordingly, a need exists for a reliable, simple, light, andinexpensive OBIGGS system for commercial aircraft application.

Moreover, the inert gas introduced into the ullage must be at arelatively low temperature. To ensure that the inert gas is at asufficiently cool temperature, current OBIGGS systems typically pre-coolthe air entering the ASM of the OBIGGS system using bulky and expensiveheat exchangers. Such a heat exchanger is shown in U.S. Pat. No.4,556,180. Accordingly, a system and method for cooling the inert airbefore it is introduced into the ullage, while eliminating the use ofbulky and costly heat exchangers, would be highly desirable.

SUMMARY OF THE INVENTION

The present invention provides a system and method for reducing thepossibility of combustion in aircraft fuel tanks by replacing air in theullage of the fuel tank with an inert gas that has been separated outfrom the engine bleed air.

In one embodiment of the invention there is provided an inert gasgenerating system. The inert gas generating system includes a compressedair source, a cooling air source, and a separation module. Theseparation module includes a housing, multiple hollow fiber membranesdisposed at least partially within the housing, first and second inlets,and first and second outlets. The first inlet is fluidly coupled to thecompressed air source, while the first outlet is fluidly coupled to thefirst inlet via the hollow fiber membranes. The second inlet is fluidlycoupled to the cooling air source, while the second outlet is fluidlycoupled to the second inlet via a space surrounding the hollow fibermembranes. The separation module also preferably includes an on-boardfilter positioned between the first inlet and the hollow fibermembranes. In addition, the inert gas generating system also preferablyincludes a filter positioned between the compressed air source and thefirst inlet. Also, a filter may be positioned between the second inletand the space. In a preferred embodiment, a valve is coupled between thecooling air source and the second inlet. A temperature sensor is alsocoupled between the cooling air source and the second inlet. Thetemperature sensor is configured to control the valve based on atemperature of the cooling air.

In another embodiment of the invention there is provided a method forgenerating inert gas. Air is firstly compressed into compressed air.Thereafter, the compressed air is introduced into multiple hollow fibermembranes. The compressed air is separated into nitrogen Enriched Air(NEA) within the hollow fiber membranes and oxygen enriched air (OEA) ina space surrounding the hollow fiber membranes. At the same time,cooling air is introduced into the space to cool the NEA within thehollow fiber membranes into cooled NEA. The cooled NEA is then expelledfrom the hollow fiber membranes, and the OEA and the cooling air isexpelled from the space. Accordingly, the present invention enhances theperformance of the system by cooling the NEA flow. This is accomplishedby transferring the heat of the NEA flow to the cooling air flow fromthe external surface of the hollow fibers. This significantly simplifiesthe system and eliminates the need for a separate heat exchanger.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing and other aspects and advantages of the present inventionwill be better understood from the following detailed description whenread in conjunction with the drawings, in which:

FIG. 1 is a schematic view of one embodiment of a modular on-board inertgas generating system according to the present invention;

FIG. 2 is a schematic view of an alternative embodiment of theinvention;

FIG. 2A is a schematic view of a further alternative embodiment of theinvention;

FIG. 3 is a cross-sectional view of a modular system according to theinvention;

FIG. 3A is a cross-sectional view of another modular system according tothe invention;

FIG. 3B is a schematic view of a modular system employing multiplemodules according to the invention;

FIG. 4 is a perspective view of an embodiment of the invention;

FIG. 5 is a schematic view of another on-board inert gas generatingsystem that includes an air separation module (ASM) incorporating acooling system, according to another embodiment of the invention;

FIG. 6 is a more detailed view of the separation module, as shown anddescribed in relation to FIG. 5; and

FIG. 7 is a flow chart of a method for obtaining an inert gas from acompressed air stream using the ASM shown in FIGS. 5 and 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As illustrated in FIG. 1, system 10 according to one embodiment of theinvention uses aircraft engine bleed air 12 that is supplied underconditions of elevated temperature and elevated pressure to generate gasfor inerting aircraft fuel tanks. It will be appreciated by personsskilled in the art that the present invention is equally useful forinerting cargo holds and other void spaces. Engine bleed air istypically supplied from taps in the compressor section of the aircraftengines at temperatures in the range of 300° F.–400° F. and at pressuresin the range of 10–45 psig depending on compressor rotation speed. It istypically used as a utility source of pressurized air on board aircraft.System 10 operates whenever bleed air is available and, thus, avoids theuse of compressors or complex control valves.

Bleed air 12 is introduced at one end of system 10 and nitrogen-enrichedair (NEA) is produced from the other end. Bleed air 12 flows underpressure and temperature to heat exchanger 14. A branch passage taps offa small portion of the pressurized bleed air to power jet pump 16. Forefficient operation, depending on size, air separation module (ASM) 18typically requires input air temperature less than about 200° F. Heatexchanger 14 is therefore used to control the temperature of the enginebleed air fed into ASM 18. Secondary cooling flow 20 is provided to heatexchanger 14 for this purpose. Jet pump 16 may be optionally utilized toprovide the cooling flow, which is vented overboard at outlet 22. Ifdesired, temperature sensor 24 may be positioned down stream of the heatexchanger to monitor output temperature and control secondary flow 20and/or jet pump 16 based on the monitored temperature.

The pressurized airflow from heat exchanger 14 enters filter 26. Filter26 may comprise multiple filters, such as a coalescing filter to removeparticulate contaminants and moisture, and a carbon filter for removinghydrocarbons. Line 28 drains removed moisture and directs it overboardat outlet 22.

After leaving filter 26, the conditioned air enters ASM 18. Typically,ASM 18 provides a total flow in the range of approximately 2–4 lbs./min.Depending on aircraft requirements or other system limitations, othersizes of ASM may be selected. Using conventional hollow-fibertechnology, ASM 18 separates the air into oxygen-enriched air (OEA) andnitrogen-enriched air (NEA). In a preferred embodiment, the ASM providesnitrogen-enriched air at flow rates between about 0.5 lbs./min. up toabout 2 lbs./min. At the lower flow rates a greater nitrogen purity canbe achieved, with oxygen making up only about one percent by volume ofthe nitrogen-enriched air. At higher flow rates the oxygen content ofthe nitrogen-enriched air is typically about nine to ten percent byvolume. Oxygen-enriched air is piped from ASM 18 overboard throughoutlet 22. Check valve 29 is provided in the overboard OEA line toprevent back-flow. Nitrogen-enriched air produced by ASM 18 is directedto the fuel tank and/or cargo hold. Orifice 30 is preferably provideddownstream of ASM 18 to control the flow rate through the ASM. Ifdesired, a stepped or variable orifice may be provided to control flowrate as described in greater detail below. Optional oxygen sensor 32 maybe configured to provide signals representing oxygen content of the NEA.Another optional sensor that may be provided is mass airflow sensor 34.This may be an automotive-style hot wire mass-flow sensor. System outlet36 directs the NEA to the fuel tank ullage and optionally to aircraftcargo hold as desired.

In an alternative embodiment illustrated in FIG. 2, engine bleed airfirst passes through an isolation valve 38. Isolation valve 38 permitssystem 10 a to be isolated from the bleed air and, if desired, may becontrolled by signals from temperature sensor 24. In this embodimentsecondary cooling air is provided by an atmospheric inlet or scoop (ramair) 40. Secondary cooling air may also be provided by an NACA scoop.Secondary cooling air passes through temperature modulation valve 42,which also may be controlled by temperature sensor 24. Alternatively,temperature control of the primary bleed airflow may be achieved througha modulated by-pass flow arrangement (described in detail with referenceto FIG. 2A). Secondary cooling air obtained from scoop 40 typically willhave a temperature ranging from about −60° F. to 110° F. or greater,depending on the environmental conditions experienced by the aircraft.The secondary airflow again passes through heat exchanger 14, optionallyassisted by jet pump 16. Operation of filter 26 and ASM 18 isessentially as described above. In this exemplary embodiment, an orificeis provided with two steps or as a stepped choke valve. For example, afirst orifice 44 presents an opening of a first size and second orifice46 presents an opening of a second size. The orifice seen by the NEAflow is determined by orifice selector 48, which may be a motor actuatedvalve. The orifice selector is utilized to control the flow rate asdescribed below. NEA exiting the system optionally passes through afirst check valve 50, after which it is directed through the fuel tankor cargo hold bulkhead 52. A second check valve 54 may be providedbefore the NEA is injected into the fuel tank or cargo hold.

The embodiments of the present invention as described above takeadvantage of characteristics of ASM 18 to produce higher purity NEA(lower 02 content) when flow is restricted. Flow may be restricted usingdown stream orifices or back pressure. In the embodiments utilizing thevariable orifices, preferably two different restrictions are used. Othernumbers might be used if warranted by system performance andrequirements. Generally, a high restriction provides low flow and highpurity, and a low restriction provides a higher flow and low purity.These embodiments rely on existing aircraft vent systems to providenormal tank inward and outward venting while mixing the NEA in the tankullage or cargo hold space. A high NEA outlet purity combined with alonger flow time will result in an ullage gas with a higher NEA purity.During the climb and cruise portion of a flight, the high purity (lowflow) NEA is delivered to the fuel tank. This stores a high nitrogenconcentration gas in the fuel tank ullage. During the descent portion ofthe flight, in which more air vents into the fuel tank as altitudedecreases, the orifice is set to provide a lower restriction and higherflow, thus producing a lower purity NEA but at greater volume. However,because high purity NEA is already stored in the fuel tank ullage, airforced in through tank vents during descent simply serves to decreasethe nitrogen purity. When supplemented by the high flow low purity NEAprovided during descent, the ullage maintains a nitrogen puritysufficient to maintain the inert condition. Given the typical commercialflight profile, although the nitrogen level decreases during aircraftdescent, with an appropriately sized system nitrogen levels can bemaintained at an inert level through aircraft landing.

In further alternative embodiments, the system of the present inventionmay be designed to eliminate components such as sensors, variableorifices and the jet pump, thereby further simplifying the system andincreasing reliability. In one embodiment, orifices 44 and 46, andselector valve 48 are eliminated by sizing the system to meet extremeoperating conditions at all times. This may be accomplished by sizingthe system to provide sufficient NEA during climb and cruise operation,so that the oxygen level in the ullage remains at below a critical levelduring descent and landing. Typically, the critical oxygen level will beless than about 10%–14% oxygen, more particularly less than about 12%oxygen. For example, if a system using the multiple orifices asdescribed above were sized to provide NEA at 0.5 lbs/min with 1% oxygenduring climb and cruise, in eliminating the orifices the system may besized to provide NEA continuously with about 2% oxygen at a slightlyhigher flow rate. Factors considered include fuel tank size and aircraftflight profile. The system is then designed to, in effect, store highpurity NEA in the fuel tank ullage so that upon inflow of air duringdescent the critical oxygen level is not exceeded before aircraftoperation ceases after landing.

In another embodiment, jet pump 16 may be eliminated by sizing thesystem to rely only on ram air from scoop 40 for secondary cooling flow.This has the advantage of further simplifying the system by removinganother component. This advantage must be balanced with the need foradditional ground service equipment to provide cooling for testing andmaintenance when the aircraft is not in flight.

Another variation involves the removal of temperature sensor 24 andtemperature modulation valve 42. In this embodiment, a maximum hottemperature is assumed based on the expected operating conditions. ASM18 is then sized to provide the required purity of NEA based on an inputtemperature at the assumed maximum.

Oxygen sensor 32 and mass flow sensor 34 also may be eliminated ifsystem health monitoring is only to be performed on the ground usingground service equipment. These alternatives for reducing systemcomplexity may be employed alone or in any combination. Exact sizing ofthe system in the various alternatives described will depend upon theinerting needs and flight profile of the particular aircraft in whichthe system is to be mounted. A person of ordinary skill in the art willbe able to match the system to the aircraft inerting needs based on thedisclosure contained herein.

In FIG. 2A, a further alternative embodiment of the invention usesprimary heat exchanger bypass flow control to control the temperature ofthe air entering the ASM inlet. Bypass valve 43 controls the airflow toheat exchanger 14 by controlling the amount of permitted bypass flow.Bypass valve 43 modulates incrementally between closed, causing allbleed air to flow through heat exchanger 14, and open, allowing theunrestricted bypass of bleed air around heat exchanger 14. The airflowallowed to bypass heat exchanger 14 follows bypass conduit 41 to the airconduit upstream of temperature sensor 24 and filter 26. Temperaturesensor 24 is, therefore positioned to determine the temperature of airentering filter 26 and ASM 18. That temperature is used to direct bypassvalve 43 to open and allow an appropriate amount of air to flow aroundheat exchanger 14 so that the temperature of the air entering filter 26and ASM 18 is within a desired temperature range. Bypass valve 43 ispreferably a phase-change direct acting mechanical sensor and flowcontrol valve. Temperature modulation valve 42 (FIG. 1) and thecorresponding control capability are added for additional temperaturecontrol if desired.

As also shown in FIG. 2A, filter 26 may include three sections. Aspreviously described, filter 26 may contain a coalescing and solidcontainment HEPA filter section, for removing particles and water, and acarbon filter section for hydrocarbon removal. In this embodiment, thefilter also includes an additional HEPA filter 27, similar to the firstfilter section, to prevent carbon filter bits from flaking off theprevious filter section and traveling to ASM 18. Subcomponentsdownstream of ASM 18 may be eliminated as shown in FIG. 2A to reducecost and complexity. In this embodiment the OEA outlet 76 exits themodule to combine with the cooling airflow downstream of the jet pump16. The filter drainpipe 28 also merges with the cooling airflowdownstream of the jet pump 16, but does so within the modular assembly.The embodiments shown in FIG. 2A are otherwise as described withreference to FIG. 2.

In a further preferred embodiment of the invention, system 10 isprovided as a modular assembly as shown in FIGS. 3 and 4. In oneembodiment, components such as ASM 18, filters 26 and heat exchanger 14are provided within common housing 60. Alternatively, housing 60 mayencompass only the ASM and filters, with the heat exchanger mountedthereon to form a single modular unit. For example band clamps 62 may beprovided between ASM 18 and filter 26, and filter 26 and heat exchanger14 to secure the components together.

At the outlet side, NEA outlet port 64 communicates with the fuel tankullage. An upper mounting bracket 66 may be provided for securing theunit in an appropriate aircraft space. At the inlet side, inlet 68receives engine bleed air 12 and directs it toward heat exchanger 14.Secondary air inlet 70 provides a secondary cooling airflow and outlet72 communicates with overboard outlet 22. Lower mount 74 also may beprovided for securing the unit. As shown in FIG. 4, OEA outlet pipe 76,secondary airflow pipe 78 and filter drainpipe 28 all lead to overboardoutlet 22. Oxygen and mass flow sensors may be provided as part of themodular unit, or separately provided, depending on space andinstallation requirements. Similarly, the orifice and associated controlvalve may be included in the modular system.

The single-housing design thus facilitates a simple, lightweightconfiguration that minimizes both acquisition, in-service andcertification costs by eliminating many of the sub-components previouslyrequired in such systems. By eliminating sub-components thesingle-housing design will also minimize installation costs whencompared to the current distributed component approach. Thesingle-housing design also improves reliability. In a preferredembodiment, the filter is arranged to be an easily replaceable,disposable cartridge, thereby enhancing maintainability.

FIG. 3A shows an additional preferred embodiment of a modular assemblywith components contained within a housing 60. In this embodiment, thecomponents are arranged so that heat exchanger 14 is between filter 26and ASM 18. Among other advantages, depending on installationrequirements, this arrangement provides better access to filter 26 formaintenance purposes. FIGS. 1 and 2 still describe the function of thisembodiment, with the internal plumbing of the various airflowsconfigured to accommodate the component arrangement in FIG. 3A.

Using the modular approach as described, a module may be designed toprovide particular, predetermined NEA flow and multiple modules employedto meet higher flow rate requirements. For example, the individualmodule may be sized to meet the inerting requirements of a particularcustomer's smallest aircraft. For larger aircraft of the same customer,instead of redesigning the module, multiple modules are employed to meetthe higher flow rate requirements. In this manner, inventory andmaintenance costs are reduced because only one type of equipment isrequired to service an entire fleet of aircraft of different sizes.

FIG. 3B shows one possible arrangement of a modular assembly employingmultiple modules. In this embodiment, five housings 60 each contain anASM 18, heat exchanger 14, and filter 26, as depicted in either of FIG.3 or 3A. The housings are plumbed together in parallel. Bleed air 12 isprovided to each heat exchanger 14 through a single isolation valve 38and a manifold 39 a. Similarly, manifold 39 b provides cooling flow 20to heat exchanger 14 and manifold 39 c collects both the OEA and thepost-heat exchanger cooling airflow and directs it overboard 22. NEA iscollected by manifold 39 d and directed to system outlet 36 and the fueltank ullage.

A further embodiment of the invention boosts system flow performance bytapping bleed air from the high-pressure segment of the aircraft's aircycle machine (ACM). Aircraft environmental control systems often use anair compressor to increase bleed air pressure and temperature in theACM. This can be used alone or in conjunction with a turbocharger toapply a significantly higher pressure to the ASM. The higher pressureincreases the flow and/or purity performance of the ASM, resulting in asmaller and less costly ASM for equivalent system performance.Alternatively, for larger aircraft, fewer ASM's may be required usingthis embodiment, again resulting in reduced costs and reducedcomplexity.

The apparatus and method of the present invention provide a moresatisfactory OBIGGS for a number of reasons. The modular approach to thedesign of the equipment reduces acquisition and installation costs. Thecartridge-style filter with quick-release installation features,together with high OBIGGS reliability due to reduced complexity, alsoreduces operational costs. The methodology of increasing NEA purity inthe tank ullage during cruise, together with increased flow/lower purityNEA injection during descent gives all of the benefits of a traditionalOBIGGS system with a much smaller, lighter, less costly, more reliablesystem.

FIG. 5 is a schematic view of another on-board inert gas generatingsystem 100 that includes a separation module 102 that also cools theoutgoing inert gas. Generally, the temperature of the compressed airentering the separation module is first lowered, as inert gas introducedinto the aircraft's fuel tanks must be at low temperatures to avoidadditional fuel vaporization. Such fuel vaporization may compound theoriginal problem of having an explosive fuel/air mixture in the ullage.Accordingly, the temperature of the compressed air is lowered before itenters the separation module. The typical source of such compressed airis bleed air that is supplied from taps in the compressor section of theaircraft engines at temperatures in the range of 300° F.–400° F.

The system 100 eliminates the need for pre-cooling the compressed airbefore is enters the ASM 102. Rather, the ASM itself acts as a heatexchanger to reduce the temperature of the separated inert gas before itis stored in the aircraft's fuel tanks.

The separation module 102 preferably includes an on-board filter 104(best seen in FIG. 6) and an on-board ASM 106, as best seen in FIG. 6.The on-board filter is similar to filter 26 (FIG. 3A) described above.Alternatively, or in addition to the on-board filter 104, a separatefilter 26 may be coupled between the source of the compressed air andthe separation module 102, as described above. The separation modulealso preferably includes a first inlet 108, a second inlet 110, a firstoutlet 112, and a second outlet 114. The first inlet 108 is coupled to acompressed air source, such as an aircraft's bleed air 103. The firstoutlet is preferably coupled to the aircraft fuel tanks or cargo areas.

The ASM 106 serves to separate inert gas, such as nitrogen, from thecompressed air, such as oxygen and water vapor. The inert gas isexpelled from the first outlet 112 as shown by arrow 116, toward thefuel tank/s, as described above.

The second inlet 110 is coupled to a cooling air source. In a preferredembodiment, this cooling air source is the ambient airflow surroundingthe aircraft. This ambient airflow is preferably captured by a scoop118, such as a NACA scoop. Alternatively, the cooling air may besupplied from a tap into another line 120 that obtains cooling air froma scoop or the like. A temperature sensor 122 measures the temperatureof the cooling air introduced into the second inlet 110. Thistemperature from the temperature sensor 122 is used to control a valve124 disposed between the source of cooling air and the second inlet 110.It should be appreciated that the temperature sensor may be positionedelsewhere, such as at second outlet 114.

The second outlet 114 is preferably coupled to an ejector 126 thatexpels the remainder of the separated air and the warmer cooling airfrom the separation module 102. The ejector 126 preferably creates anegative pressure or vacuum at the second outlet 114, thereby drawingcooling air into the second inlet 110, through the space surrounding thehollow fibers 130 (FIG. 6), and out of the second outlet 114. Theejector may be powered by the inlet pressurized air, or by internal orexternal ducting. Alternatively, the second outlet 114 may expel theremainder of the separated air and the warmer cooling air by any othersuitable means.

FIG. 6 is a more detailed view of the separation module 102 shown anddescribed in relation to FIG. 5. As can be seen more clearly in thisfigure, the compressed air or bleed air is introduced into theseparation module 102 at the first inlet 108. In a preferred embodiment,the on-board filter 104 is positioned between the first inlet 108 andthe ASM 106.

The ASM 106 preferably includes a bundle of hollow fiber membranes 130fluidly coupling the first inlet and outlet to one another. These hollowfiber membranes 130 are preferably high temperature hollow fibermembranes that are capable of withstanding typical bleed airtemperatures without requiring pre-cooling. In other words, these hollowfiber membranes 130 can withstand and operate in temperatures in excessof 300° F.

In use, compressed or bleed air flows into the first inlet 108, throughthe on-board filter 104 and into the hollow fiber membranes 130. As thecompressed airflows through the hollow fiber membranes 130, oxygen andwater vapor pass through the walls of the hollow fiber membranes 130into space 132 surrounding each of the hollow fiber membranes 130.Compressed air substantially stripped of oxygen, now mainly nitrogen,exits the hollow fiber membranes 130 and is expelled as inert gas (ornitrogen enriched air (NEA)) from the separation module 102 via thefirst outlet 112.

Also in use, cooling air from the cooling air source (described above)enters the housing at the second inlet 110. The cooling air then passesthrough the space 132 surrounding each of the hollow fiber membranes 130and is ultimately expelled from the second outlet 114. This space isdefined by the separation module's housing 138, the outer perimeter ofeach of the hollow fibers and the end walls 134. The inlets and outletsof each of the hollow fiber membranes 130 are substantially hermeticallysealed from the space 132 surrounding the hollow fiber membranes by theend walls 134.

The separation module 102 may also include another on-board filter 136for filtering the incoming cooling air prior to the cooling airflowcontacting the outside of the hollow fibers 130. Also the pressurewithin the fibers is generally kept higher than the pressure outside ofthe fibers so that separation only occurs in one direction, i.e., fromwithin the fibers to the space surrounding the fibers. Furthermore, itshould be noted that the position of the second inlet 110 and the secondoutlet 114 may be reversed. Alternatively, the second inlet 110 and thesecond outlet 114 may be positioned anywhere, as long as the secondinlet 110 and the second outlet 114 penetrate the housing 138 of theseparation module 102 between the end walls 134.

In use, the compressed air is ducted directly into the hollow fiber areawithin the module, i.e., through the hollow fibers 130, whereas thecooling airflows around the hollow fibers, i.e., flows through the space132.

FIG. 7 is a flow chart 150 of a method for obtaining an inert gas from acompressed air stream using the ASM 106 shown in FIGS. 5 and 6.Initially, air is compressed at step 152. This is preferablyaccomplished by the aircraft engine's compressor/s and extracted asbleed air. Subsequently, this compressed air is filtered at step 154,preferably by the on-board filter 104 (FIG. 6) and/or the separatefilter 26 (FIG. 6). The filtered compressed air is then introduced intothe hollow fibers 130 (FIG. 6), at step 156. The filtered compressed airis then separated, at step 158, by the hollow fibers 130 (FIG. 6) intooxygen enriched air (OEA) outside of the hollow fibers 130 (FIG. 6),i.e., in the space 132 (FIG. 6), and into nitrogen enriched air (NEA) atthe first outlet 112 (FIG. 6) of the ASM 106 (FIG. 6).

While the filtered compressed air is being separated, at step 158,cooling air is introduced into the second inlet 110 at step 160. Controlof the cooling air is regulated by the temperature sensor 122 (FIG. 5)and the valve 124 (FIG. 5), with or without a controller. This coolingair is preferably filtered by the other on-board filter 136 (FIG. 6).The cooling air passes through the space 132 (FIG. 6) surrounding thehollow fibers 130 (FIG. 6), thereby cooling the perimeter of the hollowfibers and mixing with the OEA. This cooling of the perimeter of thehollow fibers allows the hollow fibers themselves to cool the NEApassing through the hollow fibers.

The cooled NEA is then expelled from the first outlet 112 of the ASM 106at step 150. At the same time, the OEA and now warmer cooling air isexpelled from the second outlet 114 at step 162. The NEA is thenpreferably stored or introduced into the aircraft's fuel tanks or cargoareas.

The flow of cooling air around the hollow fibers may have the additionalbenefit of helping “strip” oxygen molecules from the hollow fibersurface, and also aspirate flow of the OEA to the outlet port. This inturn may help increase the efficiency of the fibers, by both applying aslight vacuum to the fiber surface, and ducting the OEA away from thesesurfaces.

Accordingly, the system 100 (FIG. 5) effectively utilizes the hollowfibers to both separate OEA from the compressed airflow source, andfunction as a heat exchanger. The input to the module is thereforecompressed air and cooling air, while the output is cooled, filtered dryNEA, and OEA which is diluted in its O₂ concentration by mixing with thecooling airflow. In this way, cool inert gas is provided without theneed for a separate heat exchanger, thereby reducing overall systemcomplexity, size, and cost.

As the separation module 102 (FIGS. 5 and 6) performs a double duty, toboth separate and cool the NEA flow, the fuel tank (or other space onthe aircraft) can be inerted by cool NEA flow without the use of a heatexchanger or temperature control system. The additional potentialbenefit is to increase the efficiency of the separation module, due toaspiration of the OEA port, and the enhancement of the flow through thespace surrounding the hollow fibers. System safety is also enhanced byensuring that cooled NEA (instead of high temperature NEA) is introducedinto the fuel tank or other space, and that OEA discharge flow isdiluted with ambient air.

The foregoing descriptions of specific embodiments of the presentinvention are presented for purposes of illustration and description.They are not intended to be exhaustive or to limit the invention to theprecise forms disclosed. Obviously many modifications and variations arepossible in view of the above teachings. For example, the separationmodule may include more or less components, such as those includedwithin the area marked by reference numeral 127. The embodiments werechosen and described in order to best explain the principles of theinvention and its practical applications, to thereby enable othersskilled in the art to best utilize the invention and various embodimentswith various modifications as are suited to the particular usecontemplated. Furthermore, the order of steps in the method are notnecessarily intended to occur in the sequence laid out. It is intendedthat the scope of the invention be defined by the following claims andtheir equivalents.

1. An inert gas generating system comprising: a compressed air sourcethat provides compressed air at an elevated temperature; a cooling airsource; a separation module; a valve coupled between said cooling airsource and said separation module; and a temperature sensor coupled tosaid valve and configured to control said valve to regulate flow ofcooling air from said cooling air source to said separation module, theseparation module further comprising: a housing; a first inlet in saidhousing, where said first inlet is fluidly coupled to said compressedair source; a first outlet in said housing for expelling inert gasenriched air, where said first outlet is fluidly coupled to said firstinlet; a second inlet in said housing, where said second inlet isfluidly coupled to said cooling air source; and a second outlet in saidhousing, where said second outlet is fluidly coupled to said secondinlet; wherein said inert gas generating system is configured to allowthe compressed air at the elevated temperature to enter said separationmodule.
 2. The inert gas generating system of claim 1, wherein saidfirst inlet is coupled to said first outlet via multiple hollow fibermembranes.
 3. The inert gas generating system of claim 2, wherein saidseparation module further comprises an on-board filter positionedbetween said first inlet and said multiple hollow fiber membranes. 4.The inert gas generating system of claim 2, wherein said hollow fibermembranes are high temperature hollow fiber membranes.
 5. The inert gasgenerating system of claim 2, wherein said multiple hollow fibermembranes extend at least partially through said housing.
 6. The inertgas generating system of claim 2, wherein said second inlet is fluidlycoupled to said second outlet through a space surrounding said multiplehollow fiber membranes.
 7. The inert gas generating system of claim 2,wherein said second inlet is fluidly coupled to said second outletthrough a space formed between said housing and said multiple hollowfiber membranes.
 8. The inert gas generating system of claim 7, furthercomprising a filter positioned between said second inlet and said space.9. The inert gas generating system of claim 1, further comprising afilter positioned between said compressed air source and said firstinlet.
 10. The inert gas generating system of claim 1, wherein saidtemperature sensor is coupled between said cooling air source and saidsecond inlet, wherein said temperature sensor is configured to controlsaid valve based on a temperature of said cooling air.
 11. The inert gasgenerating system of claim 1, wherein said cooling air source is ascoop.
 12. The inert gas generating system of claim 1, wherein saidcompressed air source is bleed air.
 13. The inert gas generating systemof claim 1, further comprising an ejector coupled to said second outletfor expelling warmed cooling air from said separation module.
 14. Aninert gas generating system comprising: a compressed air source thatprovides compressed air at an elevated temperature; a cooling airsource; a separation module; a valve coupled between said cooling airsource and said separation module; and a temperature sensor coupled tosaid valve and configured to control said valve to regulate flow ofcooling air from said cooling air source to said separation module, theseparation module having: a first inlet directly fluidly coupled to saidcompressed air source; a first outlet fluidly coupled to said firstinlet via multiple hollow fiber membranes; a second inlet fluidlycoupled to said cooling air source; and a second outlet fluidly coupledto said second inlet via a space surrounding said hollow fibermembranes, wherein said inert gas generating system is configured toallow the compressed air at the elevated temperature to enter saidseparation module.
 15. The inert gas generating system of claim 14,wherein said compressed air source is bleed air.
 16. The inert gasgenerating system of claim 14, further comprising an ejector coupled tosaid second outlet for expelling warmed cooling air from said separationmodule.
 17. The inert gas generating system of claim 14, wherein saidhollow fiber membranes are high temperature hollow fiber membranes. 18.An inert gas generating system comprising: a compressed air source thatprovides compressed air at an elevated temperature; a cooling airsource; a separation module; a valve coupled between said cooling airsource and said separation module; and a temperature sensor coupled tosaid valve and configured to control said valve to regulate flow ofcooling air from said cooling air source to said separation module, theseparation module further comprising: a housing; at least one hollowfiber membrane disposed at least partially within said housing; a firstinlet in said housing, where said first inlet is fluidly coupled to saidcompressed air source; a first outlet in said housing, where said firstoutlet is fluidly coupled to said first inlet via said at least onehollow fiber membrane; a second inlet in said housing, where said secondinlet is fluidly coupled to said cooling air source; and a second outletin said housing, where said second outlet is fluidly coupled to saidsecond inlet via a space surrounding said at least one hollow fibermembrane, wherein said inert gas generating system is configured toallow the compressed air at the elevated temperature to enter saidseparation module.
 19. The inert gas generating system of claim 18,wherein said compressed air source is bleed air.
 20. The inert gasgenerating system of claim 18, further comprising an ejector coupled tosaid second outlet for expelling warmed cooling air from said separationmodule.
 21. The inert gas generating system of claim 18, wherein said atleast one hollow fiber membrane is a high temperature hollow fibermembrane.
 22. An inert gas generating system comprising: a separationmodule comprising: a housing; a first inlet in said housing, whereinsaid first inlet is configured to be directly fluidly coupled to acompressed air source that provides compressed air at an elevatedtemperature; a first outlet in said housing configured to expel inertgas enriched air; at least one hollow fiber membrane extending at leastpartially through said housing and fluidly coupling said first inlet tosaid first outlet; a second inlet in said housing, wherein said secondinlet is configured to be fluidly coupled to a cooling air source; and asecond outlet in said housing, where said second outlet is fluidlycoupled to said second inlet through a space surrounding each of saidhollow fiber membranes, wherein said inert gas generating system isconfigured to allow the compressed air at the elevated temperature toenter said separation module; a valve coupled between said cooling airsource and said separation module; and a temperature sensor coupled tosaid valve and configured to control said valve to regulate flow ofcooling air from said cooling air source to said separation module. 23.The inert gas generating system of claim 22, wherein said compressed airsource is bleed air.
 24. The inert gas generating system of claim 22,further comprising an ejector coupled to said second outlet forexpelling warmed cooling air from said separation module.
 25. The inertgas generating system of claim 22, wherein said hollow fiber membranesare a high temperature hollow fiber membranes.
 26. A method forgenerating inert gas comprising: compressing air into compressed air atan elevated temperature; introducing said compressed air at the elevatedtemperature into multiple hollow fiber membranes; separating saidcompressed air into Nitrogen Enriched Air (NEA) within said hollow fibermembranes and Oxygen Enriched Air (OEA) in a space surrounding saidmultiple hollow fiber membranes; injecting cooling air into said spaceto cool said NEA within said hollow fiber membranes into cooled NEA;expelling said cooled NEA from said hollow fiber membranes; measuring anair temperature; and regulating flow of said cooling air injected intosaid space based on said air temperature.
 27. The method of claim 26,wherein said compressing comprises compressing ambient air using acompressor of an aircraft engine.
 28. The method of claim 26, furthercomprising, prior to said introducing, filtering said compressed air.29. The method of claim 26, further comprising, prior to said injecting,filtering said cooling air.
 30. The method of claim 26, furthercomprising storing said NEA.
 31. The method of claim 26, furthercomprising introducing said NEA into an aircraft fuel tank.
 32. Theinert gas generating system of claim 1, wherein said housing includes atubular side wall and first and second end walls, wherein said firstinlet and first outlet are disposed in a respective one of said firstand second end walls and said second inlet and second outlet aredisposed in said tubular side wall.
 33. The inert gas generating systemof claim 18, wherein said housing includes a tubular side wall and firstand second end walls, wherein said first inlet and first outlet aredisposed in a respective one of said first and second end walls and saidsecond inlet and second outlet are disposed in said tubular side wall.34. The inert gas generating system of claim 22, wherein said housingincludes a tubular side wall and first and second end walls, whereinsaid first inlet and first outlet are disposed in a respective one ofsaid first and second end walls and said second inlet and second outletare disposed in said tubular side wall.
 35. An inert gas generatingsystem comprising: a compressed air source; a cooling air source; aseparation module comprising: a housing; a first inlet in said housing,where said first inlet is fluidly coupled to said compressed air source;a first outlet in said housing for expelling inert gas enriched air,where said first outlet is fluidly coupled to said first inlet; a secondinlet in said housing, where said second inlet is fluidly coupled tosaid cooling air source; and a second outlet in said housing, where saidsecond outlet is fluidly coupled to said second inlet; a valve coupledbetween said cooling air source and said second inlet; and a temperaturesensor also coupled between said cooling air source and said secondinlet, where said temperature sensor is configured to control said valvebased on a temperature of said cooling air.